1. Field of the Invention
The present invention relates to a light emitting device, and more particularly, to an AC light emitting device, which can be driven by being connected directly to an AC power source.
2. Discussion of the Background
With the development of GaN based light emitting diodes (LEDs), the GaN based LEDs have considerably changed LED technologies. Currently, the GaN based LEDs are used for various applications such as full-color LED displays, LED traffic lights, white LEDs and the like. Recently, it has been expected that high-efficiency white LEDs will substitute for fluorescent lamps. In particular, the efficiency of white LEDs has reached the level similar to that of typical fluorescent lamps.
In general, an LED emits light by forward current and requires the supply of DC. Hence, if the LED is connected directly to an AC power source, it is repeatedly turned on/off depending on the direction of current. As a result, there are problems in that the LED does not continuously emit light and is easily broken by reverse current.
To solve such a problem, an LED capable of being connected directly to a high-voltage AC power source is disclosed in PCT Patent Publication No. WO 2004/023568(A1), entitled “LIGHT-EMITTING DEVICE HAVING LIGHT-EMITTING ELEMENTS” by SAKAI et al.
According to PCT Patent Publication No. WO 2004/023568(A1), LEDs (i.e., light emitting cells) are two-dimensionally connected in series on a single insulative substrate such as a sapphire substrate to form LED arrays. Such two LED arrays are connected to each other in reverse parallel on the sapphire substrate. As a result, there is provided a single chip light emitting device capable of being directly driven by an AC power supply.
However, in the single chip light emitting device, a failure of any one of the light emitting cells connected in series or disconnection/short circuit of wires results in a chip failure that makes the AC operation of the device impossible. In particular, in a cast that the single chip includes a few tens of light emitting cells and wires for connecting them in series and reverse parallel so as to be driven under a high voltage, e.g., a 110/220V AC power source used for general household, a chip failure may be easily occurred due to a large number of the light emitting cells and the wires formed on the single chip.
Further, as a plurality of light emitting cells are connected in series and reverse parallel on the same substrate, it is likely that short circuits between wires for connecting the light emitting cells increase, and the processes of patterning the light emitting cells are complicated.